1. Field of the Invention
The present invention relates to a medical monitoring apparatus used for remotely monitoring an electrocardiogram and respiration of a subject by a digital telemeter. More particularly, the invention relates to a medical monitoring apparatus capable of automatically checking an interference.
2. Related Art
There is known a medical monitoring apparatus used for remotely monitoring an electrocardiogram and respiration of a subject. Depending on the form of the signal processed, the medical monitoring apparatus is categorized as being either of the analog type or of the digital type. To check its receiving condition, the analog medical monitoring apparatus uses an intensity of an electric field of the receiving signal, while the digital medical monitoring apparatus detects presence or absence of a channel ID.
In the communication between the transmitter and the medical monitoring apparatus, there is a case where an intensity of an electric field of a signal received from the transmitter is excessively decreased. This is caused, for example, when something is wrong with the transmitter, a battery is flat, a distance between the transmitter and the medical monitoring apparatus is too long. In this case, the analog medical monitoring apparatus displays a message of no reception. The medical monitoring apparatus is frequently used, together with other medical apparatuses. These other medical apparatuses, when operating, emit radio waves. The analog medical monitoring apparatus is sensitive to these interference radio waves leaking from the other medical apparatuses. When any of the interference radio waves is more intensive than the radio wave received from the transmitter, the medical monitoring apparatus mistakenly recognizes the interference radio wave as its intended radio wave and displays it as the intended data signal. This phenomenon is called a radio interference.
The digital medical monitoring apparatus also displays "no reception" when it cannot discriminate a channel ID for the reason that something is wrong with the transmitting system including the transmitter or the receiving system including the medical monitoring apparatus. No reception is displayed also when the medical monitoring apparatus fails to discriminate a channel ID by the interference.
Thus, when interference occurs, the analog medical monitoring apparatus displays the waveform of the interference radio wave from another medical apparatus, and the digital medical monitoring apparatus displays no reception. In other words, neither of the conventional medical monitoring apparatuses can distinctly show the interference.
As described above, when the radio wave leaking from another medical device, used near the medical monitoring apparatus, has a frequency equal to that of a radio wave used in the medical monitoring apparatus, interference occurs. In this case, the conventional medical monitoring apparatus can indistinctly show the interference. In other words, any of the conventional medical monitoring apparatuses cannot clearly show the cause of an erroneous signal in the medical monitoring apparatus, i.e., the failure in the transmitting system and/or the receiving system or interference.